1. Field of the Invention
The present invention relates to a semiconductor device and more particularly, to a bonding structure of a semiconductor element and a semiconductor element mounting member.
2. Description of the Prior Art
A bonding structure of a semiconductor element and a semiconductor element mounting member is known in, for example, Japanese Patent Laying-Open Gazettes No. 14557/1983, No. 61055/1984, No. 169160/1984, No. 177953/1984, No. 177594/1984, No. 747/1985, No. 8934/1986 and No. 123162/1986, and Japanese Utility Model Laying-Open Gazette No. 118252/1985. Japanese Patent Laying-Open Gazette No. 14557/1983 discloses a semiconductor device in which a semiconductor chip mounted on a die attach portion of a lead frame is resin molded, characterized by providing a through hole in the die attach portion. Japanese Patent Laying-Open Gazette No. 61055/1984 discloses a semiconductor device wherein a concave portion is formed on a mounting substrate and a semiconductor chip is mounted to cover the concave portion through a mounting material with which the concave portion is filled. Japanese Patent Laying-Open Gazette No. 169160/1984 discloses a semiconductor device wherein a tub to which a pellet is attached is provided with an elongate transparent hole for separating a pellet attaching portion from a tub lead. Japanese Patent Laying-Open Gazette No. 177953/1984 discloses a semiconductor device wherein a groove for absorbing a stress is formed in the corner portion on the lower surface of a bed on which a semiconductor pellet is mounted, to disperse a stress which is produced at the time of heat tratment so that occurrence of a crack is prevented. Japanese Patent Laying-Open Gazette No. 177954/1984 discloses a semiconductor device wherein a concave portion for absorbing a stress is formed in the peripheral region on the lower surface of a bed on which a semiconductor pellet is mounted, to absorb a stress which is produced at the time of heat treatment in the concave portion so that occurrence of a crack is prevented. Japanese Patent Laying-Open Gazette No. 747/1985 discloses a resin molder IC package wherein the bonding area of a die lead frame on the bottom surface of an IC chip is limited to be smaller than the base area of the IC chip. Japanese Patent Laying-Open Gazette No. 8934/1986 discloses a semiconductor device wherein a large-sized pellet is attached to a pellet attaching surface by a bonding material, characterized in that a plurality of grooves are formed on at least one of the rear surface of the pellet and the pellet attaching surface. Japanese Patent Laying-Open Gazette No. 123162/1986 discloses a lead frame wherein through holes are provided in portions to be resin molded of a bed supporting portion and a lead portion and a lot of concave portions are provided on the rear surface of a bed portion so that a peripheral edge of the bed portion has a complicated concave and convex shape and the portion to be resin molded of the bed supporting portion is wound. Japanese Utility Model Laying-Open Gazette No. 118252/1985 discloses a lead frame for resin molded semiconductor having a disk shaped island with a semiconductor chip being disposed on one surface of the island and a plurality of leads extending outward from the vicinity of the island, characterized in that the other surface of the island has a concave portion or a feed-through portion.
FIGS. 1 and 3 are plan views showing the vicinity of a semiconductor element mounting portion of a conventional semiconductor device, FIG. 2 is a cross-sectional view showing a semiconductor device taken along a line I--I shown in FIG. 1, FIG. 4 is a cross-sectional view showing a semiconductor device taken along a line II--II shown in FIG. 3. In FIGS. 1 to 4, a semiconductor element 1 is mounted on a semiconductor element mounting member 2 which is a mounting portion of a lead frame and bonded by a bonding material 3. Each bonding electrode 4 of the semiconductor element 1 is wire-bonded to an external terminal 6 by a wiring material 5.
The semiconductor element 1 has recently been large-scaled. In order to improve the heat dissipation characteristic, the semiconductor element mounting member 2 is formed of a copper or copper containing material. Since coefficient of thermal expansion of a copper or copper containing material is much different from that of the semiconductor element, there is a problem that if the entire surface of the semiconductor element 1 is bonded by the bonding material 3 as shown in FIGS. 1 and 2, a thermal stress is produced as the temperature changes after bonding, so that a crack occurs in the semiconductor element 1.
Furthermore, when in order to prevent the crack, the semiconductor element 1 is partially bonded as shown in FIGS. 3 and 4, a stress is reduced. However, since the semiconductor element 1 is partially floating from the semiconductor element mounting member 2, the semiconductor element 1 may incline before the bonding material is solidified. In such a case, the wiring material 5 can not be stably attached to the semiconductor element 1.